A windshield wiper linkage is used in order to transmit motion from a motor, via an output spindle of a speed reduction unit, to at least one driving spindle of a windshield wiper. Essentially the linkage consists of several coupling links connected to each other. For layout reasons, the reduction gear spindle often has to lie in a plane which is not parallel to the plane passing through the drive axis of the wiper, which is why the various coupling links must be connected through ball and socket type couplings. The latter not only enable one link to rotate with respect to another, but also allow for a certain amount of angular displacement between any two links. These couplings are commonly in the form of a ball carried by one end of one coupling link and articulated in a ball socket which is carried by another end of another link.
As described for example in the specification of U.S. Pat. No. 3.704,903, a hole is provided in one end of the coupling link, the hole being generally perpendicular to the plane of this end portion, and a ball socket is moulded on to the end portion around the hole. For this purpose, partial circumferential grooves are formed concentrically with the orifice, so that during the moulding operation the material in which the ball socket is moulded can be introduced into these grooves. The socket will then be anchored in the end portion of the link and any parasitic circumferential movement of the ball socket will be prevented.
However, the assignee of the present applicant have found that such an arrangement has a major drawback. This is that, during the moulding operation, the amount of moulded plastics material varies from one part to another of the longitudinal plane of the end portion of the link and in its vicinity. The effect of this, during cooling of the material and as a result of the inherent asymmetry of the moulding operation, is that shrinkage of the moulded material leads to irregular variations in thickness of different portions of the ball socket, and this in turn can adversely affect the anchoring of the ball socket on the base member comprising the remainder of the link.